This invention relates to a no-carbon pressure-sensitive copying paper having a microcapsule coating layer obtained by using a special binder and being excellent in color developing properties, resistance to smudges and high concentration coating suitability.
No-carbon pressure-sensitive copying paper is usually produced by coating micro-capsules containing colorless leuco dyes in several microns to ten-odd microns in diameter on a support. Sometimes, the micro-capsules and a color developer are coated on supports separately and used as a top sheet and a bottom sheet, or alternatively the micro-capsules and the color developer are coated on both sides of a support and used as an intermediate sheet. When a plurality of these sheets are piled with a proper combination and a physical pressure is applied thereto by handwriting, typewriting, or the like to rupture the micro-capsules, the leuco dye in the micro-capsules is in contact with a developer to form a color, which results in giving a recorded image.
Major conditions generally required for producing no-carbon pressure-sensitive copying papers and quality thereof are as follows:
(1) A dense and clear image can be obtained in a short time and not deteriorated with the lapse of time.
(2) When color development is not desired, for example, during the production process of no-carbon pressure-sensitive paper, during printing and cutting steps, or during storage or handling in the form of sheets or wind-up state, there take place no smudges.
Since the above-mentioned two requirements are contradictory, it is difficult to satisfy the both requirements sufficiently at the same time. But the improvement therefor has been tried and proposed, for example, by changing production conditions of micro-capsules, changing the kind and amount of buffering agents, changing the kind and amount of binders. No satisfactory results are obtained.
On the other hand, in the production of not only pressure-sensitive copying paper but also coated paper, the concentration of coating solutions is tried to be made higher in order to lower the energy necessary for drying the coated paper to the utmost and to increase the coating speed. As a means for attaining such objects, there have been proposed an improvement in properties of coating solutions, an improved process for coating, or the like. Particularly, in the production of pressure-sensitive copying paper, there have been proposed a process for using a low viscosity microcapsule emulsion, a process for using a low viscosity binder, a process for scraping a coating solution, and the like. For example, the use of a latex as a binder is shown in Japanese Patent Unexamined Publication Nos. 61- 268481, 61-273985, and 61-280985. But resistance to smudge due to friction is still insufficient. Even combining the above-mentioned means to carry out high concentration coating, the resulting pressure-sensitive copying paper is lowered in resistance to smudge due to friction in practical use. This results in greatly damaging the quality of no-carbon pressure-sensitive copying paper.
As mentioned above, the quality of no-carbon pressure-sensitive copying paper is greatly influenced by not only formulation of coating solutions but also coating methods and coating solution concentrations. No no-carbon pressure-sensitive copying paper improved in the above-mentioned defects has been obtained.